1. Field of the Invention
This invention relates to a method for yarn piecing in a fasciated yarn spinning unit.
2. Description of the Prior Art
Significant improvements have been made in fasciated yarn spinning recently, resulting in high processing speeds of as much as 150 m/min.
In fasciated yarn spinning, a fiber bundle is twisted by a vortex while passing through a channel of an air nozzle. In the structure of the yarn thus obtained, a plurality of surface fibers are entangled around a core portion having substantially no twist.
Due to the above-mentioned double structure of the yarn, however, there is a serious problem with yarn piecing. The tensile strength of the fasciated yarn mainly depends on the binding effect of the surface fibers around the core portion. Accordingly, it is impossible to piece a yarn merely by overlapping the broken end with the fiber bundle as is the case of ring spinning. The broken end of the yarn has to be intermingled with the fiber bundle and twisted together for ensuring complete piecing.
Japanese Unexamined Patent Publication No. 53-35033 discloses a yarn piecing method for a fasciated yarn spinning unit comprising the steps of introducing a broken end of a yarn reversely into an air nozzle for twisting a fiber bundle, nipping the end between a pair of front rollers of drafting means disposed adjacent to the air nozzle, starting the drafting means to advance a fiber bundle, and simultaneously applying compressed air to the air nozzle to generate a vortex therein, whereby the broken end of the yarn and the fiber bundle are pieced together during passage through the air nozzle.
In this prior art, however, the broken end and the fiber bundle cannot be fully intermingled, which causes failure of piecing or a weak and/or conspicuous joint in the resultant yarn.